Metallic wires are widely used in medical procedures, a common example being the guidewires used to locate intravascular devices such as angioplasty catheters. Conventional guidewires for angioplasty and other vascular procedures usually comprise an elongated core member with one or more tapered sections near the distal end thereof and a flexible body such as a helical coil disposed about the distal portion of the core member. A shapable member, which may be the distal extremity of the core member or a separate shaping ribbon which is secured to the distal extremity of the core member extends through the flexible body and is secured to a rounded plug at the distal end of the flexible body. Torquing means can be provided on the proximal end of the core member to rotate, and thereby steer, the guidewire while it is being advanced through a patient's vascular system.
A major requirement for guidewires and other guiding members, whether comprising solid wire or tubular members, is that they have sufficient column strength to be pushed through a patient's vascular system or other body lumens without kinking. However, they must also be flexible enough to avoid damaging the blood vessel or other body lumen through which they are advanced. Commonly, guidewires are formed from two or more materials. A relatively short, distal section is configured to have superior handling characteristics and may be shaped to aid in selecting the desired branch of the vasculature. The relatively long proximal section, on the other hand, should have a high column strength and torquability as its primary characteristic. Accordingly, prior art guidewires have been made with stainless steel alloys such as 304V stainless steel which can have a composition which includes about 10% nickel. Such alloys can also be used for the entire length of the guidewire. Although widely used, some stainless steel alloys suffer from being relatively brittle and are subject to fatigue. In addition, the nickel content can be a drawback for patients who are sensitive to this element.
Accordingly, there is a need for guidewire materials having high tensile strength, while maintaining good ductility, fracture toughness and high number of fatigue cycles and strength. It can also be desireable to have a guidewire material with a low nickel content.